Anyone watching television or reading the daily paper over the past decade or so could hardly be blamed for thinking climate science a murky affair, rife with disagreement and doubtful claims. One ‘expert’ is pitted against another, the first muttering something about solar flares and the other trying to explain what ‘peer review’ means. But there hasn’t been real disagreement in reputable scientific circles on climate change for some time. Remaining arguments are about fine details. But it’s easy – and comforting – to find a marginal crackpot on television telling us not to worry. That’s irresponsible journalism, and gives an impression of doubt where none exists.

The basics of climate science have been settled in the scientific community for years: we know the earth is warming, we know it’s our carbon dioxide emissions causing it, and we know that – without big reductions in emissions – the climate will change in ways that are harmful to our way of life.

It’s often claimed this knowledge is doubtful. Because it is based on ‘theories’, it can be dismissed as conjecture. That is to mistake what is meant by ‘theory’. It is scientific theory that the earth is round, and it is a theory the sun will rise in the east tomorrow. To science all knowledge is refutable, given the right evidence. Every theory has a degree of doubt. If one day the sun rose in the west, theories about planetary movement would be changed. The real issue is – what is the degree of doubt?

It’s true that climate science is complex. But one of the largest international assemblies of scientists ever formed – the Intergovernmental Panel on Climate Change (IPCC) – agree on the basics. Even the slightest chance they are right would warrant serious action, a kind of insurance policy against calamity. But the chances of the IPCC being correct is not slim – you can bet your house on it. Here are some basics.

Carbon dioxide[i] (carbon) in the atmosphere warms the earth, acting as a insulating blanket. It lets in more energy as sunlight than it lets out as heat, trapping the heat. We’ve known this since the early 1800’s[ii]. Without greenhouse gases the earth would be inhospitable – but there can be too much of a good thing!More than 100 years ago scientists began to worry, calculating how much carbon burning coal emitted and how much it might warm the atmosphere. Emissions then were tiny, and it remained a theoretical curiosity.

Carbon concentrations are linked with temperature over long periods of time[iii]. Carbon concentrations – measured in parts per million (ppm) – weremeasured directly starting in the 1950s, and measurements going back hundreds of thousands of years are made possible by looking at tiny bubbles trapped in Antarctic ice. The deeper in the ice you go, the further back in time the air was trapped. Temperature is calculated by measuring the ratio of two kinds of molecules – oxygen and deuterium – set by the temperature at the time the air was trapped. We know that when carbon goes up, so does temperature[iv]. There are other ways to confirm this link, like looking at ancient tree rings or the sediment on the bottom of deep lakes. They all say the same thing.

Carbon levels are rising fast, and human activity is responsible.De-forestation and fossil fuel use are what is changing the game. The carbon concentration has risen from pre-industrial levels of 280 ppm to more than 390 ppm, higher than it’s been for hundreds of thousands of years. It’s still rising 3 ppm a year. We know we’re responsible because we know how much carbon we release, and we know how much is absorbed[v]. Roughly – the difference is us. Really dangerous levels of carbon occur around 450 ppm, so without big changes we’ll be there when today’s pre-schoolers are attending university.

We are causing the latest warming, which is happening alarmingly fast[vi]. Average world-wide temperatures have risen by 0.6 oC in the last century, the fastest rise in the last thousand years. The rise is directly co-related to the rise in carbon. Temperature cycles in the past that saw ice ages come and go were caused by subtle changes in the orbit of the earth (called Milankovich cycles), but that is not the case now. Those cycles are regular, we known when they occur – and this isn’t it.

The future looks bleak if we don’t change our behaviour[vii]. Warming is not a gradual, gentle process that lets Torontonians wear shorts in December and lengthens the golf season in New York State. It disrupts ecosystems, causes violent storms and changes weather patterns. It will render life very difficult. That story continues in Climate Science III –The Bad Stuff.

Finally – this stuff is coming at us faster than is generally acknowledged in the popular media. The IPCC is authoritative, but conservative[viii].The latest science shows we’re already past their worst-case scenarios. Stuff that wasn’t supposed to happen for decades is happening before our eyes, like the summer melting of Arctic ice and permafrost, and the recent droughts in Australia.

[i] There are other greenhouse gases – methane, nitrous oxide and water vapour , among others – but for simplicity I shall stick to carbon dioxide as it contributes more than 60% of the greenhouse effect.

[ii] For an historical account of this discovery, see http://www.aip.org/history/climate/co2.htm

[iv] Sometimes the temperature goes up first, then carbon rises, which caused some people to doubt the link. What this shows, though, is the existence of ‘feedback mechanisms’ where an increase in temperature causes something to happen (like the melting of permafrost that holds stored carbon) that releases more carbon. See Climate Science III -The Complex Stuff for details on feedback.

[vii] For a full account of what might happen in the climate see G. Monbiot’s Heat, and for the geopolitical sphere, see G. Dyer’s Climate Wars.

[viii] The IPCC was saddled at the outset by a need to generate an unusually high degree of consensus – near unanimity – before it publishes any results. It takes time to build that consensus, and the outcome is rendered very conservative.It also takes a great deal of time to go through the rigorous peer-review process. The end result is they use data that is, literally, years out of date. For the 2007 report, field data from the turn of the century was used.